1. Field of the Invention
This invention relates to irrigation solution for use in ophthalmological surgery, and more particularly to intraocular irrigation solutions having good compatibility with ocular tissues.
2. Description of the Prior Art
In intraocular surgery it is conventional to supply to the surgical field a continuous flow of liquid to replace fluid lost from the interior of the eye. In surgery performed in the anterior chamber of the eye, e.g., in cataract extraction, it is necessary to supply fluid to the anterior chamber to prevent collapse of the chamber with consequent injury to tissues, particularly to the delicate corneal endothelium. Furthermore in some surgical procedures, e.g., phacoemulsification wherein the tissue of the cataractous crystalline lense is broken up, the irrigation fluid serves to carry away fragmented tissue from the surgical site. In posterior chamber surgery, e.g., in vitrectomy, the material removed from the chamber must be replaced with fluid in order to keep the surgical field clear and maintain the volume of the eyeball. In early ophthalmological surgical procedures wherein the time of surgery was relatively short, the intraocular tissue were exposed to the irrigation fluid for a relatively short period of time. Hence, a simple irrigation solution such as physiological saline solution was used. Such as osmotically adjusted solution prevented damage to the tissues due to osmotic shock, did not closely approximate the actual physiological intraocular fluid. As more extensive and longer surgical procedures within the eye began to be performed, the intraocular tisues were exposed for a relatively long time to the irrigation solution, and it became apparent that a solution having a composition closer to that of the natural intraocular fluid, e.g., the aqueous humor of the anterior chamber, was desirable in order to prevent damage to intraocular tissues deprived of their customary surrounding fluid. Accordingly, a number of irrigation solutions have been developed which are believed to be more compatible with the physiology of ocular tissues than physiological saline. For example, lactated Ringer's solution has been used, wherein some of the sodium chloride of physiological saline has been replaced with potassium chloride, calcium chloride and sodium lactate. A further development is balanced salt soluton (BSS), which also includes potassium, calcium and magnesium and an acetate-citrate buffer system, but no lactate. BSS, however, contains no energy source, is slightly hypotonic and has an alkaline pH. Another solution developed for intraocular irrigation is glutathione-bicarbonate-Ringer's solution (GBR), which incorporated reduced glutathione to provide a source of energy for intraocular cells, particularly for cells of the corneal endothelium, in order to maintain these delicate and critical cells in good condition during long surgical procedures. While GBR is an effective intraocular irrigating solution, it is somewhat unstable because the reduced glutathione becomes oxidized during storage and use. In order to overcome this problem a variation of GBR has been developed which uses oxidized glutathione together with glucose to provide a source of energy which the cells may use to produce the reduced glutathione they need.
Each of these irrigation solutions has utility in particular situations. However, ocular tissue also has a need for ascorbate and the aqueous humor is known to contain ascorbate, but the irrigation solutions used hitherto have omitted ascorbate. Hence these solutions have not been able to replace the ascorbate lost during surgery, and a need has continued to exist for an ophthalmic irrigating solution for intraocular surgery which more closely approximates the composition of the natural aqueous humor within the eye.